DESCRIPTION: The formation of synapses in the CNS and PNS is a very precise and elegant interaction between a presynaptic nerve terminal and its postsynaptic target. The neuromuscular junction has proven to be a good model for synapse formation throughout the body. During development, a motor neuron sends out a process to contact its target muscle fiber where it induces the formation of the postsynaptic apparatus. The postsynaptic apparatus includes aggregates of the receptor for acetylcholine (AChRs), acetylcholinesterase (AChE), specific cytoskeletal proteins, and basal lamina. There is good evidence that the motor nerve terminal releases the protein agrin which induces the formation of this postsynaptic apparatus. The protein agrin has a dual nature, with one arm of the protein it binds to synaptic basal lamina, while with another arm it simultaneously interacts with its receptor on the surface of the muscle fiber. In order to understand the mechanisms that control the formation and stabilization of synapses it will be critical to understand how agrin binds to basal lamina. Just as critical will be to understand how agrin is removed from the synaptic basal lamina once it is bound. The results of these experiments will allow us to test specific mechanisms that control synapse formation and elimination. The specific aims of this proposal are: 1. Characterize the binding of agrin to synaptic basal lamina molecules and identify these agrin- binding basal lamina molecules. 2. Characterize the distribution of agrin molecules during synapse formation, elimination, regeneration and remodeling at the neuromuscular junction. 3. Generate antisera that is specific for agrin released by nerve terminals.